Stabilized hydro-mechanical pressure control valve



Sept. 15, 1970 w s 3,528,454

STABILIZED HYDRO-MECHANICAL PRESSURE CONTROL VALVE Filed Nov. 29, 1968 INVENTOR:

United States Patent O 3,528,454 STABILIZED HYDRO-MECHANICAL PRESSURE CONTROL VALVE Ernest E. Lewis, Topsfield, Mass., assignor to General Electric Company, a corporation of New York Filed Nov. 29, 1968, Ser. No. 779,796 Int. Cl. F16k 11/07 US. Cl. 137625.69 Claims ABSTRACT OF THE DISCLOSURE A hydraulic network is provided in a hydro-mechanical pressure control valve including a sleeve and a spool with a plurality of lands thereon to produce close time correspondence between an input shaft and the difference in pressure at output ports thereof. The network includes a cylinder having a pair of outlets between which an orifice is connected and a piston. The piston is mechanically coupled to the input shaft of the valve and the two outlets are hydraulically coupled to chambers formed by the sleeve and lands. Also, the input shaft and the spool shaft are proportional to render the force on the input shaft constant and in addition means are provided for reducing the magnitude of such constant force.

The present invention relates, in general, to hydromechanical pressure valves and more particularly to hydromechanical pressure control valves which are stabilized by hydro-mechanical means.

In electrohydraulic systems, stabilization is provided therein by tachometer transducers and electrical stabilizing networks. Such stabilizing transducers and networks enable fast response and good performance to be obtained in such systems. Heretofore, hydro-mechanical servo systems either utilized electro-hydraulic stabilizing networks or did not employ stabilizing networks. When electrohydraulic networks are utilized in such systems, a source of electrical power is required and additional complexity is introduced into the system by the added components. Accordingly, such networks are not commonly used in hydro-mechanical servo systems with a result that their performance is inferior to that of the more complex electro-hydraulic servo systems.

An object of the present invention is to provide an improved hydro-mechanical pressure control valve for use in hydro-mechanical servo systems.

Another object of the present invention is to provide a hydro-mechanical pressure control valve which is stabilized to provide close correspondence between input mechanical displacement and resultant output pressure dilferential corresponding to a particular displacement of the input.

Another object of the present invention is to provide a means in a hydro-mechanical pressure control valve for rendering the force required to produce a displacement substantially independent of the displacement of the input thereof.

Another object of the present invention is to provide hydro-mechanical means in a hydro-mechanical pressure control valve for reducing the force required to produce input displacement,

In carrying out the objects of my invention in one illustrative form thereof there is provided a main cylinder in which is contained a spool having an intermediate and a pair of end lands to form with the cylinder a pair of intermediate chambers and a pair of end chambers. A pair of end cylinders are secured to the main cylinder and contain spring biasing elements supporting the shaft of.the spool in the axial directions. A pair of feedback passages are provided between each of the end cylinders 3,528,454 Patented Sept. 15, 1970 "ice and a remotely positioned intermediate chamber. A source port and a pair of drain ports are located on the main cylinder. In the null position of the spool the source port registers with the intermediate land, and each of the drain ports registers with a respective end land. A pair of output ports is provided each connected to a respective intermediate chamber. An input shaft is provided within the remote wall of one of the end caps and contacts one of the bias springs. A piston is provided on the input shaft which in turn is housed in an auxiliary cylinder.

- One side of the cylinder is connected to an adjacent end chamber of the main cylinder and the other side of the cylinder is connected to the other end chamber in the main cylinder. An orifice is provided between the two ends of the auxiliary cylinder. Accordingly, an aiding force is provided on the spool which is a function of the rapidity of the displacement of the input shaft thereby maintaining a close time correspondence between axial displacement of the input shaft and difference in pressure in the output ports corresponding to such displacement. In addition, in accordance with another aspect of the present invention, by proportioning the cross-sectional area of the input shaft to be twice the cross-sectional area of the spool shaft, the force required to displace the input shaft is made independent of the displacement thereof.

The novel features which are believed to be characteristic of the present invention are set forth in the appended claims. The invention itself, however, together with further objects and advantages thereof may best be understood by reference to the following description taken in connection with the accompanying drawings in which:

The figure is a schematic view in cross section of an embodiment of my invention.

In the figure, there is illustrated a pressure control valve 10 in accordance with my invention incorporated in a control system in which a mechanical angular displacement of an input lever 11 about a pivot point 12 produces a certain rate of change of angular displacement of an output lever 13 about another point 14. The lever 11 is connected to an input shaft 15. A piston 16 is connected to the output lever 13 and is movable in a cylinder 17 in response to a difference in pressure at the output ports '18 and 19 of the valve 10. The valve 10 includes a main cylinder 20 having a pair of end walls 21 and 22 and a pair of end cylinders 23 and 24 each including a pair of end walls, and axially aligned on each side of the main cylinder 20 in fixed relationship thereo. A spool 30 is provided in the main cylinder 20 consisting of a shaft 31, and intermediate land 32, and a pair of end lands 33 and 34- mounted thereon. The lands and the main cylinder form a pair of intermediate chambers 25 and 26 and a pair of end chambers 27 and '28. A source port 60 and 'a pair of drain ports 61 and '62 are located on the main cylinder 20. In the null position of the spool, the source port 60 registers with the intermediate land 32, drain port 61 registers with end land 33, and drain port 62 registers with end land 34. The shaft 31 of the spool 30 is supported in the end walls of the main cylinder 20 and has one end extending into end cylinder 23 and has the other end extending into the other end cylinder 24. An auxiliary cylinder 35 consisting of a central section and a pair of end walls is also provided and is axially aligned and secured in fixed relationship to the end cylinder 23. A shaft 15 with a piston 37 thereon is movably mounted in the cylinder 35. A pair of ports 38 and 39, each connected to a respective one of the chambers formed between the piston 37 and the auxiliary cylinder 35 is provided. A pair of centering springs 40 and 41 is provided. Spring 40 is mounted in end cylinder 23 between ends of the shafts 31 and 15 extending therein. The other spring 41 is mounted between the other end of the shaft 31 and the end wall of end cylinder 24. The other end of the second shaft is connected to input lever 11 as mentioned above. Another piston 45 is provided on the shaft between the input lever 11 and the auxiliary cylinder 35 and is contained within a second auxiliary cylinder 46 in fixed relationship to the first auxiliary cylinder 35,- having a central section and a pair of end walls through which the shaft 15 extends. A pair of outlets 47 and 48 are provided to end chambers formed by the piston 45 and the cylinder 46.

Each of output ports 18 and 1.9 is connected by pas sageways 50 and 51 to a respective remotely situated end cylinder to provide feedback thereto. Orifices 52 and 53 may also provided to dampen oscillations in the valve, if needed. A duct 54 is provided connecting port 38 of auxiliary cylinder 35 to adjacently located end chamber 27 in the main cylinder and another duct 55 is provided connecting port 39 of the auxiliary cylinder to the other end chamber 28. An orifice 36 is provided across ports 38 and 39. A passageway 56 is provided from port 48 of the second auxiliary cylinder 35 to the drain port 61. Another passageway 57 is provided from port 47 of the second auxiliary cylinder to the source port 60.

With a spool in the null position, the pressures P and P in outlets 18 and 19 are equal. The force tending to move the spool 30 to the left is the compression of the spring 41. In the steady state condition, this force is counteracted by the pressure differential across the force compensation piston 45 and the input force on the shaft 15 which is transmitted through the spring 40. Moving the input lever 11 to the right compresses spring 40 and forces the spool 30 to move to the right. The

piston 37 is also moved to the right causing a compression of the fluid in the cylinder and a pressure drop across the orifice 36. The pressure differential in cylinder 35 acts on the spool 30 to cause it to move to the right. This additional force which is a function of the velocity of the input shaft 15 decreases the time for the spool to move to ultimate position thereby decreasing the phase lag between the input motion of shaft 15 and the output pressure differential P -P i.e., it provides a time correspondence between input shaft 15 displacement and output pressure differential even for rapid displacements. Of course, when the lever 11 is released, the pretensioning springs and 41 return the input shaft 15 to its starting position and the spool 30 is returned to its null position.

The proportioning of the active area of the piston 37 and the cross-sectional area of the orifice 36 in relation to the cross-sectional area of the end face of the land 33 depends upon the response desired in the servo system in which the valve is connected. The valves of the areas of the auxiliary piston 37, the end land 33 and the cross-sectional area of the orifice 36 are selected to give the desired stable response, i.e., a design with the desired phase margin. When the area of the piston 37 is large in relation to the cross-sectional area of the orifice 36, a larger pressure drop is produced between the outlet ports 38 and 39 of the auxiliary cylinder for a given displacement of the shaft 15, thereby producing a close correspondence in the motion of the shaft 15 and the shaft number 31 with the result that the output pressure differential is in close time correspondence with input shaft motion. Similarly, when the area of the piston 37 is large in relation to the area of the end face of the land 33, a stiffer or more faithful time correspondence between input motion and output pressure differential is obtained. The impedance provided by the orifices should be small in relation to the impedance to fluid flow provided by the end seals in the end cylinder 23 which seal the shafts 15 and 31. Leakage through such end seals affects the gain of the valve. Should the valve have oscillations in certain applications, orifices 52 and 53 may be introduced into the feedback passageways and 51 to dampen any such oscillations.

The force required to move the input shaft 15 depends on the pressure exerted by spring 41 and pressure feedback on spool 30 as will be apparent from the analysis below. In accordance with another aspect of the present invention, by making the cross-sectional area of shaft 15 equal to twice the cross-sectional area of the shaft 31, the force required to move the shaft 15 is made independent of the position of the shaft 15, that is, it is constant with input shaft displacement.

In accordance with a further aspect of the present invention, a means is provided to counterbalance the afore mentioned constant force. To this end a piston 45 and cylinder 46 are provided. The piston 45 and the second auxiliary cylinder 46 when energized with fluid under pressure from the pressure supply, provides a force on shaft 15 to reduce the force required to move the spool 30. However, as seals must be provided and frictional forces are inherently involved in such seals, the force cannot be practically reduced to zero.

The operation of the invention will be more fully appreciated by considering the equations governing the operation of the servo valve. Steady state force on shaft 15 is given by the following equation:

where F=the force on the shaft 15,

C 'is the constant representing the pretension force on the springs 40 and 41 when the spool is in the null or neutral position,

k =spring gradient,

Y=displacement of shaft 15,

A =cross-sectional area of the shaft 15,

P designates the cross-over pressure,

P designates the pressure at outlet 18,

P designates the pressure at outlet 19,

P designates supply pressure,

A is the cross-sectional area of the shaft 31 and is referred to as the feedback area,

A is equal to the effective area of the piston 45 To simplify the derivation it will be assumed that the pretension force C is zero and the force A P on the second cylinder is zero. Terms representing these factors can readily be inserted in the final equation.

In deriving the aforementioned Equation 1 the following assumptions are made:

(1) The motion of the spool 30 is neglected, that is, Y is much greated than where X is the displacement of the spool from its neutral or null position.

(2) Cross-over pressure At null pressure differential, that is, when the spool 30 is in the neutral or null position, P =P =P and neglecting pretension in the springs 40 and 41.

The force on shaft 15 is given by the following equation:

and hence 2k, AF

The pressure again is given by the relationship Fi i Y AF Substituting Equation 5 in Equation 3 and rearranging terms yields the following relationship:

A PZ k, A P F' 2 AI 2 or as it is assumed that x is much smaller than Y and noting that the cross-over pressure is equal to the following equation is obtained:

While I have shown a particular embodiment of my invention it will, of course, be understood that I do not wish to be limited thereto since many modifications may be made in the structural arrangement shown and in the instrumentalities employed. I contemplate by the appended claims to cover any such modifications as fall Within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A fluid pressure control valve comprising a main cylinder, a pair of end cylinders, an auxiliary cylinder, each having a hollow central section and a pair of end walls,

said cylinders being aligned on an axis in fixed relationship to one another, each end cylinder being adjacent to a respective end wall of said main cylinder and one of said end cylinders being adjacent to said auxiliary cylinder,

a first shaft axially aligned in said main cylinder and having each end extending through a seal in a respective end wall thereof into a respective end cylinder, said shaft having a pair of end lands and an intermediate land mounted on said shaft to form with said main cylinder a pair of intermediate chambers and a pair of end chambers,

a second shaft axially mounted in said auxiliary cylinder having one end thereof extending through a seal in an end wall thereof adjacent to said one end cylinder thereinto and having the other end thereof extending through a seal in the other end wall to a point external to said auxiliary cylinder, a piston mounted on said second shaft in said auxiliary cylinder,

a first spring mounted in said one end cylinder between one end of said first shaft and said one end of said second shaft,

a second spring mounted between the other end of said first shaft and said other end cylinder,

a pair of passageways each connecting a respective end cylinder to a respective intermediate chamber remotely located with respect thereto,

a fiuid supply port connected to said main cylinder, said port being blocked by said intermediate land when in its null position, a pair of fluid drain ports connected to said main cylinder, said ports being blocked by said end lands when in their central position, a pair of outlet ports each connected to a respective intermediate chamber,

a pair of ducts, one duct connecting an end of said auxiliary cylinder adjacent to said main cylinder to an adjacent end chamber thereof, the other of said ducts connecting the other end of said auxiliary cylinder to the other of said end chambers, a passageway having an orifice therein connected between said ducts, whereby a rapid displacement of said second shaft develops a pressure differential between said outlet ports in close time correspondence therewith.

2. The combination of claim 1 in which the active area of an end wall of said piston in relation to the cross-sectional area of said orifice is sufiiciently large to produce a buildup of suflicient pressure in an end chamber in response to rapid displacement of said second shaft to maintain a close time correspondence between axial displacement of said second shaft and difference in pressure in said output ports corresponding to such axial displacement.

3. The combination of claim 1 in which the active area of an end wall of said piston is substantially greater than the active area of an end wall of an end land.

4. The combination of claim 1 in which the impedance to fluid flow of said orifice is substantially less than the impedance to fluid flow provided by shaft seals in said one end cylinder.

5. The combination of claim 1 in which is included a pressure differential utilization device connected to said outlet ports.

6. The combination of claim 1 in which the crosssectional area of said second shaft is twice the crosssectional area of said first shaft, whereby the force re quired to displace said second shaft is independent of the displacement thereof.

7. The combination of claim 1 including a second auxiliary cylinder having a hollow central cylinder and a pair of end walls axially aligned with said first axial cylinder and in fixed relationship therteo, said second shaft extending through seals in the end walls thereof, another piston mounted on said second shaft in said second auxiliary cylinder, and

a second pair of ducts, one of said ducts connecting an end of said second auxiliary cylinder adjacent said main cylinder to said drain ports, the other of said ducts connecting the other end of said second auxiliary cylinder to said supply port, the cross-sectional area of said second shaft being twice the cross-sectional area of said first shaft.

8. The combination of claim 7 in which said first auxiliary cylinder is located between said one end cylinder and said second auxiliary cylinder.

9. The combination of claim 1 in which fluid damping means are provided in each of said passageways.

10. A fluid pressure control valve comprising a main cylinder, a pair of end cylinders, an auxiliary cylinder, each having a hollow central section and a pair of end walls,

said cylinders being aligned on an axis in fixed relationship to one another, each end cylinder being adjacent to a respective end wall of said main cylinder and one of said end cylinders being adjacent to said auxiliary cylinder,

a first shaft axially aligned in said main cylinder and having each end extending through a seal in a respective end wall the eof into a respective end cylinder, said shaft having a pair of end lands and an intermediate land mounted on said shaft to form with said main cylinder a pair of intermediate chambers and a pair of end chambers,

a second shaft axially mounted in said auxiliary cylinder having one end thereof extending through a seal in an end wall thereof adjacent to said one end cylinder thereinto and having the other end thereof extending through a seal in the other end wall to a point external to said auxiliary cylinder, a piston 7 mounted on said second shaft in said auxiliary cylinder,

a first spring mounted in said one end cylinder between a. pair of passageways each connecting a respective end cylinder to a respective intermediate chamber remotely located with respect thereto,

a fluid supply port connected to said main cylinder, said port being blocked by said intermediate land when in its null position, a pair of fluid drain ports connected to said main cylinder, said ports being blocked by said end lands when in their central position, a pair of outlet ports each connected to a respective intermediate chamber, and

pair of ducts, one duct connecting an end of said auxiliary cylinder adjacent to said main cylinder to said drain ports, the other of said ducts connecting the other end of said auxiliary cylinder to said supply port, the cross-sectional area of said second shaft being twice the cross-sectional area of said first shaft, whereby the force required to displace said second shaft is independent of the displacement thereof.

7 References Cited UNITED STATES PATENTS 2,621,676 12/1952 Loft "137-6256 3,003,474 10/1961 Giles et a1. 137-62563 XR 3,237,641 3/1966 Audemar 137596.15

HENRY T. KLINKSIEK, Primary Examiner US. Cl. X.R. 

